A NATO statement says the four died Monday when a roadside bomb exploded in eastern Afghanistan. The statement does not give nationalities, but U.S. spokesman Lt. Robert Carr confirms all four were Americans.

No further details were released. A British soldier was killed Sunday in southern Afghanistan.

Those deaths bring to at least 55 the number of international troops killed in Afghanistan in July, the deadliest month of the war for the NATO mission.

At least 30 U.S. troops have died this month—three more than the death toll for September 2008 which had been the deadliest month for the American force in Afghanistan.

Last year at this time there were only about 30,000 U.S. troops in the country. Today there is double that, and many more U.S. aircraft. Two of the six recent incidents involved American aircraft.